Thinner for rinsing photoresist and method of treating photoresist layer

ABSTRACT

A thinner for rinsing photoresist including 50 to 80 wt. % of n-butyl acetate, propylene glycol alkyl ether, and propylene glycol alkyl ether acetate, is provided. The thinner is neither toxic to humans nor ecologically undesirable and has no unpleasant odor. The waste solutions thereof and associated waste water are easily handed so as to render this thinner environmental friendly. Additionally, the photoresist thinner of the present invention has excellent rinsing ability.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application is based on application No 99-62169 filed in theKorean Industrial Property Office on Dec. 24, 1999, the content of whichis incorporated hereinto by reference.

BACKGROUND OF THE INVENTION

[0002] (a) Field of the Invention

[0003] The present invention relates to a thinner for rinsingphotoresist and a method of treating a photoresist layer and, moreparticularly, to a thinner for rinsing an edge of photoresist layer on asubstrate, such as a liquid crystal display substrate or a semiconductorsubstrate and a method of treating a photoresist layer using the thinner

[0004] (b) Description of the Related Art

[0005] For producing tiny circuit patterns such as those used in liquidcrystal display (LCD) circuits or semiconductor integrated circuits, aphotoresist composition including a polymer resin, a photosensitivecompound and a solvent is uniformly coated or applied on an insulatorlayer or a conductive metal layer on a substrate and the coated orapplied substrate is then soft-baked to evaporate the solvent. Thesoft-baked substrate is selectively exposed to some form of radiation,such as ultraviolet light, electrons, or X-rays, and the exposedsubstrate is then hard-baked. Next, the hard-baked substrate isdeveloped to produce a desired pattern. The developed substrate isetched with a mask to remove the insulator layer or the conductive metallayer and the residual photoresist layer is removed to complete thetransfer of the tiny pattern onto the substrate surface.

[0006] Since the photoresist layer on the edge of the substrate is lessuniform than in the substrate central areas, the uneven of thephotoresist layer or beads should be removed from a wafer and thesubstrate should then be cleaned.

[0007] Both mechanical and chemical processes are known for the removalof the uneven excess photoresist or beads, but these processes leavemuch to be desired. If the cured coating is mechanically stripped as byscraping, the removal of the material is almost invariable accompaniedby some physical damage. Alternatively, the cured coating is chemicallystripped as by stripping, cleaning or thinning with a thinner Thethinner may generally be methyl isobutyl ketone (MIBK).

[0008] This compound has good ability to rinse photoresist, but it istoxic to humans and the environment and is restricted in its use by ISO14000. Accordingly, there is a need to replace methylisobuthylketonewith other materials.

[0009] U.S. Pat. No. 4,983,490 discloses a photoresist treatingcomposition. The composition includes 1 to 10 parts by weight ofpropylene glycol alkyl ether (PGME) and 1 to 10 parts by weight ofpropyelene glycol alkyl ether acetate (PGMEA). The composition, however,has poor ability to rinse photoresist and has a lower photoresistsolubility and evaporation rate than MIBK.

[0010] There is still a need for a thinner for rinsing photoresist whichis not toxic to humans, ecologically undesirable, and has no unpleasantodor, and which can also quickly and completely remove cured or uncuredphotoresist layer from the substrate without resulting in thecontamination thereof and damage.

SUMMARY OF THE INVENTION

[0011] It is an object of the present invention to provide a thinner forrinsing photoresist, which is not toxic to humans and has no unpleasantodor.

[0012] It is another object to provide a thinner for rinsingphotoresist, which is environmentally friendly so that the wastesolution and waste water thereof is easily treated.

[0013] It is still another object to provide a thinner for rinsingphotoresist, which exhibits excellent ability to rinse photoresistlayer.

[0014] It is still yet another object to provide a thinner for rinsingphotoresist, which can be stored at room temperature and can be usedwithout changing conventional equipment and production conditions.

[0015] It is also another object to provide a method of treatingphotoresist layer using the thinner.

[0016] These and other objects may be achieved by a thinner for rinsingphotoresist including 50 to 80 wt % of n-butyl acetate, propylene glycolalkyl ether, and propylene glycol alkyl ether acetate.

[0017] In order to achieve these objects and others, the presentinvention provides a method of treating a photoresist layer. In thismethod, a photoresist composition is coated on a substrate. Thephotoresist composition includes a polymer compound, a photosensitivecompound and a solvent. The photoresist layer is then rinsed with athinner for rinsing photoresist. The thinner includes 50 to 80 wt % ofn-butyl acetate, propylene glycol alkyl ether, and propylene glycolalkyl ether acetate. It is preferred that a soft-baking step is furtherperformed by heating the photoresist coated on the substrate before therinsing step.

[0018] The present invention further includes a method of producing atiny circuit pattern for a liquid crystal display circuit or asemiconductor circuit. In this method, a photoresist composition iscoated on a substrate for a liquid crystal display or a semiconductor.The photoresist composition includes a polymer compound, aphotosensitive compound, and a solvent. The photoresist composition onthe substrate is heated to evaporate the solvent from the compositionand the heating step is called a “soft-baking step”. As the result, aphotoresist layer is formed on the substrate. The photoresist layer onthe substrate is selectively exposed to some form of radiation, such asultraviolet light, electrons, or X-rays through a mask to produce apattern. The exposed substrate is then dipped into a developing aqueoussolution to dissolve the exposed or unexposed photoresist layer and thisstep is called a “developing step”. The developed photoresist layer isheat-treated and the heating step is called a “hard-baking step”. Next,the hard-baked substrate is etched to produce a circuit pattern and tostripe the residual photoresist. The photoresist layer is rinsed using athinner for rinsing photoresist after any one of the steps of coating,soft-baking, exposing, developing, or hard-baking. The thinner includes50 to 80 wt % of n-butyl acetate, propylene glycol alkyl ether, andpropylene glycol alkyl ether acetate

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] A more complete appreciation of the invention, and many of theattendant advantages thereof, will be readily apparent as the samebecomes better understood by reference to the following detaileddescription when considered in conjunction with the accompanyingdrawings, wherein:

[0020]FIG. 1 is a graph illustrating dissolution rate of thinnersaccording to one embodiment and a comparative example of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

[0021] A thinner of this invention includes n-butyl acetate, propyleneglycol alkyl ether, and propylene glycol alkyl ether acetate. Thethinner includes preferably, 50 to 80 wt %, more preferably 60 to 70 wt% of n-butyl acetate, preferably 15 to 30 wt %, more preferably 20 to 30wt % of propylene glycol alkyl ether and preferably 5 to 20 wt %, morepreferably 5 to 15 wt % of propylene glycol alkyl ether acetate.

[0022] If the amount of n-butyl acetate is less than 50 wt %, theevaporation rate and photoresist solubility is reduced. Whereas, if theamount thereof is more than 80 wt %, the evaporation rate and ability topermeate is increased too much. If the amount of propylene glycol alkylether is less than 15 wt %, the evaporation rate and ability to permeateis increased too much. Whereas, if the amount thereof is more than 30 wt%, the evaporation rate and photoresist solubility is reduced. If theamount of propylene glycol alkyl ether acetate is less than 5 wt %, theevaporation rate and ability to permeate is increased too much. Whereas,if the amount thereof is more than 20 wt %, the evaporation rate andphotoresist solubility is reduced.

[0023] Toxicity tests and ignition and explosive tests for methylisobutyl ketone (MIBK) (conventionally used as a thinner), n-butylacetate (n-BA), propylene glycol alkyl ether (PGME), and propyleneglycol alkyl ether acetate (PGMEA) that are used for the thinner of thepresent invention were performed and the results are presented in Tables1 and 2. TABLE 1 Toxicity test TWA Solvent [ppm] STEL [ppm]Toxicological Information MIBK  50  75 LD₅₀/oral/mouse: 2080 mg/kgLD₅₀/dermal/rabbit: 20 mg/kg or more LD₅₀/inhal/mouse: 23300 mg/m³LC_(lo)/inhal/rat: 4000 ppm n-BA 150 200 LD₅₀/oral/rat: 14000 mg/kgLD₅₀/inhal/rat: 2000 ppm (4 hrs) PGME 100 N. A. LD₅₀/oral/rat: 6600mg/kg LD₅₀/dermal/rat: 13000 mg/kg LC₅₀/inhal/rat: 5000 ppm (7 hrs)PGMEA 100 N. A. LD₅₀/oral/rat: 8532 mg/kg LD₅₀/dermal: 5000 mg/kgLC₅₀/ingal/rat: 4245 ppm (6 hrs)

[0024] TWA (time weighted average): average concentration to whichnearly all employees could be repeatedly exposed without adverse effectsfor 8 hours a day and for 40 hours a week

[0025] STEL (short term exposure limit): concentration to whichemployees can be exposed for short term (15 minutes) without inducingnarcosis or stimulation, either of which can lead to accidents and adecreases of work efficiency.

[0026] LD₅₀ (lethal dose 50): the dose of a substance which is fatal to50% of the test animals

[0027] LC_(lo) (Lethal Concentration Low): the lowest concentration of asubstance in air which has been reported to have caused death in humansor animals for periods of exposure which are less than 24 hours

[0028] N.A.: non-available TABLE 2 Ignition and Explosive Tests Vaporpressure Flash Evaporation [mmHg]/ point Boiling Ignition ExplosiveSolvent rate temperature [° C.] [° C.] point [° C.] point [° C.] limit[%] MIBK 1.57  16/20 18 115 449 1.4 to 7.5 n-BA 0.98 7.8/20 22 126 4251.7 to 15 PGME 0.66 6.7/20 32 120 N.A. 2.7 to 11.8 PGMEA 0.34 3.8/20 42146 354 1.5 to 7

[0029] In Table 2, the evaporation rate is indicated by a relative valueby setting the evaporation rate of butyl acetate to be equal to one, andthe explosive limit is indicated by the concentration range at whichflame propagation occurs under a suitable firing source. As shown inTables 1 and 2, n-BA used in the present invention shows superiorbiological and physical safety characteristics to those of MIBK used inthe conventional process and shows the same or as good biological andphysical safety characteristics as those of PGME or PGMEA.

[0030] A photoresist composition for producing a photeresist layer iswell known in the related art. A photoresist composition includes apolymer compound, a photosensitive compound, and a solvent, with a goodexample thereof being a, novolak resin. Useful photosensitivediazide-based compounds may be produced by reacting polyhydroxybenzophenon with diazide-based compounds, such as1,2-naphtoquinonediazide or 2-diazo-1-naphtol-5-sulfonic acid. Thesolvent in the photoresist composition generally includes xylene, butylacetate, cellosolve acetate, propylene glycol alkyl ether acetate, or amixture thereof.

[0031] The photoresist composition may be coated on a semiconductor or aLCD substrate by general coating techniques such as immersing, spraying,rotating and spinning steps. Examples of the substrate materials aresilicone, aluminum, silicone dioxide, silicone nitride, tantalum,copper, polysilicon, ceramic, and various polymerable resins. When thephotoresist is coated on the substrate, particularly by spin coating,the uneven portions, such as beads on the edge of the substrate, arecaused due to photoresist lumps.

[0032] The thinner for rinsing the photoresist of the present inventionis sprayed on the substrate such that beads are dissolved and a uniformphotoresist layer can be produced. Alternatively, the photoresist layeris dipped into the thinner such that the thickness of the photoresistlayer can be controlled. The rinsing step also may be performed after asubsequent soft-baking step or hard-baking step.

[0033] The coated substrate is heated at 20 to 100° C. to perform asoft-baking step. This step permits the evaporation of the solventwithout pyrolysis of a solid component in the photoresist composition,and is performed until the solvent is mostly evaporated in order toproduce a thin coating layer of the photoresist composition on thesubstrate.

[0034] Next, the substrate coated with the photoresist layer isselectively exposed to a form of radiation, such as ultraviolet light,electrons, or X-rays using a suitable mask to obtain a desirablepattern. The exposed substrate is then dipped into an aqueous alkalinedeveloping solution until either the exposed or unexposed photoresistlayer (depending on the type of photoresist) is all or almost entirelydissolved. The exposed or unexposed photoresist removed substrate isthen taken out from the developing solution. The resulting substrate isthen heat-treated to improve adhesion and to increase chemicalresistance of the photoresist layer and this step is called hard-bakingstep. The developed substrate is treated with an etchant or with vaporplasma to etch the exposed portion and the residual photoresist protectsthe substrate regions which it covers. The photoresist layer is removedfrom the etched substrate using a stripper to complete the transfer thepattern onto the substrate surface.

[0035] The following examples further illustrate the present invention.

EXAMPLE 1 AND COMPARATIVE EXAMPLE 1

[0036] Two wafers coated with photoresist were dipped into a thinnercomposition and a thinner. The thinner composition included 65 wt % ofn-BA, 24 wt % of PGME, and 11 wt % of PGMEA, and the thinner wascomposed of MIBK. The complete photoresist removal times (i.e., no traceof photoresist existing after drying) were measured and the results arepresented in Table 3. TABLE 3 Example 1 Comparative example 1 Completephotoresist 18 18 removal time [sec]

EXAMPLE 2 AND COMPARATIVE EXAMPLE 2

[0037] 1.7 g of thinner composition and 1.7 g of thinner wererespectively poured into two aluminum dishes and allowed to stand for 32minutes. The thinner composition included 65 wt % of n-BA, 24 wt % ofPGME, and 11 wt % of PGMEA and the thinner was composed of MIBK. Theresidual weight of the thinner composition and the thinner wererespectively measured, and the results are shown in Table 4. TABLE 4Example 2 Comparative example 2 Residual weight after 32 6 0 minutes (wt%)

[0038] As shown in Tables 3 and 4, the thinner composition of thepresent invention has a lower volatility and has similar photoresistsolubility when compared with MIBK.

EXAMPLE 3 AND COMPARATIVE EXAMPLE 3

[0039] The photoresis composition was coated on two Si wafers and asoft-baking step was performed at 140° C. for 90 seconds to obtain aphotoresist layer with a thickness of 2.09 μm on the wafer. Theresulting wafers were dipped into a thinner composition and a thinner,respectively. The thinner composition included 65 wt % of n-NA, 24 wt %of PGME, and 11 wt % of PGMEA and the thinner was composed of MIBK. Thethickness of the layer according to the time was measured and theresults are shown in FIG. 1. As shown in FIG. 1, the photoresist thinnerof Example 3 shows good photoresist solubility and low build-up andpermeation properties when compared with MIBK.

EXAMPLE 4 AND COMPARATIVE EXAMPLE 4

[0040] A photoresist composition was coated on a tetragonal glasssubstrate for a liquid crystal display device and a soft-baking step wasperformed to produce a photoresist layer. A edge portion of thephotoresist layer was rinsed with a thinner composition including 65 wt% of n-BA, 24 wt % of PGME, and 11 wt % of PGMEA, and with MIBK,respectively. The profile of the photoresist produced on four sides ofthe photoresist layer (correspond to observation points 1, 2, 3 and 4)was scanned with a surface scanner and the build-up and permeation ofthe photoresist layer was determined. The results of this scanning arepresented in Table 5. The build-up value is indicated by height of theedge portion in the rinsed photoresist layer and the permeation value isindicated by horizontal distance from the edge to a portion of which thesurface appearance is modified by the permeation of the thinner. TABLE 5Example 6 Comparative example 6 Observation Permeation Build-upPermeation point Build-up [μm] [μm] [μm] [μm] 1 333 4.02 3.49 4.20 21.30 2.48 1.65 2.54 3 2.48 2.68 1.80 2.98 4 1.52 1.98 2.58 2.20 Average2.16 2.79 2.38 2.98

[0041] The photoresist thinner of Example 6 shows a lower build-up andpermeation properties when compared with MIBK. The results indicate thatthe thinner of the present invention can rinse the edge portion of thephotoresist layer without resulting in a modification thereof.

[0042] The thinner for rinsing photoresist of the present invention isneither toxic to humans nor ecologically undesirable and has nounpleasant odor. The waste solutions thereof and associated waste waterare easily handed so as to render this thinner environmental friendly.Additionally, the photoresist thinner of the present invention hasexcellent rinsing ability.

[0043] While the present invention has been described in detail withreference to the preferred embodiments, those skilled in the art willappreciate that various modifications and substitutions can be madethereto without departing from the spirit and scope of the presentinvention as set forth in the appended claims.

What is claimed is:
 1. A thinner for rinsing photoresist comprising: 50to 80 wt % of n-butyl acetate; propylene glycol alkyl ether; andpropylene glycol alkyl ether acetate.
 2. The thinner of claim 1 whereinthe amount of n-butyl acetate is 50 to 80 wt % based on the totalcomposition, the amount of propylene glycol alkyl ether is 15 to 30 wt %based on the total composition, and the amount of propylene glycol alkylether acetate is 5 to 20 wt % based on the total composition.
 3. Amethod of treating a photoresist layer, comprising the steps of: coatinga photoresist composition on a substrate, the photoresist compositionincluding a polymer compound, a photosensitive compound, and a solvent;rinsing the photoresist layer with a thinner for rinsing photoresist,the thinner including 50 to 80 wt % of n-butyl acetate, propylene glycolalkyl ether, and propylene glycol alkyl ether acetate.n-butyl acetate.4. The method of claim 3 further comprising a step of soft-baking beforethe rinsing step, the soft-baking step being performed by heating thephotoresist layer on the substrate.
 5. A method of producing a liquidcrystal display or semiconductor circuit, comprising the steps of: (a)coating a photoresist composition on a substrate for a liquid crystaldisplay or a semiconductor, the photoresist composition including apolymer compound; a photosensitive compound, and a solvent (b)soft-baking, wherein the coated substrate is heated to evaporate thesolvent from the composition and to produce a photoresist layer on thesubstrate; (c) selectively exposing the soft-baked substrate through amask to produce a pattern; (d) developing, wherein the exposed substrateis dipped into a developing aqueous solution to dissolve an exposed orunexposed photoresist layer (e) hard-baking, wherein the developedphotoresist layer is heat-treated; (f) etching the hard-baked substrateto produce a circuit pattern and to strip the residual photoresist; and(g) rinsing the photoresist layer using a thinner for rinsingphotoresist after any one step of (a) to (e) steps, the thinnerincluding 50 to 80 wt % of n-butyl acetate, propylene glycol alkylether, and propylene glycol alkyl ether acetate.
 6. The method of claim5 wherein the rinsing step is performed by spraying the thinner to thephotoresist layer to remove an edge of the photoresist layer.
 7. Themethod of claim 5 wherein the rinsing step is performed by dipping thephotoresist layer into the thinner to control the thickness of thephotoresist layer.
 8. The method of claim 5 wherein the coating step isperformed by dipping the substrate in the composition, or by spraying orspin-coating the composition on the substrate.
 9. The method of claim 5wherein the substrate is selected from the group consisting of silicone,aluminum, silicon dioxide, silicon nitride, tantalum, copper,polysilicon, ceramic, and polymerizable resin.